1. Field of the Invention
The present invention relates to a photocatalytic material consisting of titanium or a titanium alloy coated with an oxide film having a photocatalytic activity.
2. Background Art
A titanium oxide of an anatase type has a photocatalytic activity, which is utilized for decomposing harmful substances such as nitrogen oxides (NOx) or bacteria. Such a photocatalytic material is also excellent in appearances so as to be used for decorative applications. In recent years, there have been great demands for improving the photo catalytic materials to have a higher photocatalytic activity and more excellent appearances.
One way to produce a photocatalytic material is to anodize a substrate consisting of titanium or a titanium alloy in an electrolyte. For instance, there has been known method comprising a step of anodizing a titanium substrate in an aqueous phosphoric acid solution for covering the surface thereof with an anatase type titanium oxide, which is described in Japanese laid Patent Application (JP-A) No.08-246192 and No. H10-121266. These anodization methods however may yield the anatase type titanium oxide poorly. Therefore, the treated substrate further has to be coated on its surface with anther active anatase type titanium oxide for providing a sufficient photocatalytic activity.
In light of the above situation, it is an object of the present invention to reexamine the prior art methods to provide a method for producing a photocatalytic material comprising a titanium oxide, the photo catalytic material having a higher photo catalytic activity and more excellent appearances.
The inventor of the present invention has repeated various investigations to solve the above problem. As a result, the inventor has found that the above problem can be solved by a method for preparing a photocatalytic material according to the present invention. The method comprises a step of oxidizing the surface of a substrate consisting of titanium or a titanium alloy. This method also comprises steps of anodizing the substrate in an electrolyte containing an organic acid and/or any salt of the organic acid, and oxidizing the anodized substrate in an atmosphere.
This method may further comprise a step of immersing the substrate in an aqueous solution containing a peroxide before anodizing the substrate.
The present invention differs from current anodization methods in the point that a substrate is anodized in an electrolyte containing an organic acid or salt thereof, then oxidized in an atmosphere. The present invention also differs from current anodization methods in the point that the substrate is in advance pretreated in an aqueous solution containing a peroxide.